A light-emitting device using luminescence from an electrolight-emitting element (light-emitting element) is attracting attention as a device for display or illumination. As a light-emitting element used in a light-emitting device, a light-emitting element having a structure in which a layer containing a light-emitting compound is sandwiched between a pair of electrodes is well known. In such a light-emitting element, one electrode serves as an anode while the other serves as a cathode. Then, a hole injected from the anode and an electron injected from the cathode are recombined to form an excited molecule, and light is emitted when the excited molecule returns to a ground state.
In a display device to be incorporated in various kinds of information processing appliances which have developed rapidly in recent years, reduction of power consumption is particularly required, and it has been attempted to decrease the drive voltage of a light-emitting element in order to achieve the low power consumption. Further, in view of commercialization, not only the decrease in the drive voltage but also the extension of lifetime of a light-emitting element is significant. Therefore, development of a light-emitting element to achieve the extension of lifetime has been advanced.
For example, in Patent Document 1 (Japanese Patent Application Laid-Open No. H9-63771), the decrease in drive voltage of a light-emitting element has been achieved by forming an anode with metal oxide having high work function such as molybdenum oxide. Moreover, an advantageous effect of long lifetime is also obtained.
However, in order to extend the lifetime, a means shown in Patent Document 1 is not enough and technical development to achieve the longer lifetime has been required. Moreover, since a light-emitting element is usually formed with a thin film of about sub-micrometer thick, such a light-emitting element has a problem in that an upper electrode and a lower electrode are easily shorted. In particular, low yield due to dust generated in a manufacturing process of a light-emitting element is a problem.